I have a 400ex it runs fine but when it idles it's not consistent but it backfires through the carb sometimes it shuts off sometimes it just kills the motor down a little cleaned the carb twice, cleaned the filter, set the valves, checked the timing, still can't figure it out and when you ride it it's fine only when it idles it does this if anyone can help me out I'd appreciate it

I would check for a intake leak, such as a torn carb boot or something. Next the intake valves could be to tight and not closing the valves all the way.

Ok I'll check that thanks

Checked them the valves look good and intake does but going to replace oring anyway any other ideas

when u cleaned the carb did u check the pilot jet ? if u didnt that may be ur prob.

My ol ladys 400ex had the same kinda issue and it was a plugged pilot jet. The carb is a CS to get off, and as I remember the jets are goofy as all get out in side, but once you find them all and get them cleaned up it should be good.

I pulled that carb apart 3 times and cleaned when the bike first came to me that's what thought pilot jet it was dirty and the main jet so I cleaned the whole put it back on and the same thing I checked and double checked even triple checked the carb, valves, filter, timing, intake, cdi box. I guess the only thing that is left is something in the wiring I do know it's not the cdi box and it idles goofy its just got me puzzled

The stock boots separate and it's hard to see you might have to pull it off to see it.

Jets are cheap. And make sure you blow out all the air passages with air compressor.

Try moving up the pilot jet up to the next size.

Ok I'll try those things and see what happens thanks for the info